It is known that machines for extracting a beverage from a particulate substance usually require that the particulate substance is placed into a filtering receptacle installed in the machine. In particular, automatic or semiautomatic espresso coffee machines comprise a filtering receptacle, also called filter holder, in which a dose of ground coffee is placed before the extraction of coffee beverage takes place.
The general steps for extracting a coffee beverage in an espresso coffee machine, which are substantially equivalent to those of other automatic machines for preparing a beverage starting from an edible substance, comprise a phase of delivering hot water under suitable pressure into an extraction chamber which includes the filtering receptacle, followed by a brewing phase and a phase of conveying the brewed beverage into an external cup, jug or glass, ready to drink.
Ground coffee, as well as other edible substances for preparing beverages, is usually a single use substance, in that the organoleptic qualities such as taste, aroma and body of the brewed beverage are irremediably lost once ground coffee has been soaked. Accordingly, in espresso coffee machines and in other brewing machines the edible substance has to be removed after one single brewing. This is the reason why the filtering receptacle housing a dose of ground coffee is usually manually removable from the espresso coffee machine, in order to allow emptying of the receptacle from the used ground coffee and filling it with a new dose of ground coffee.
In order to facilitate the operations of filling and emptying the filtering receptacle, single serving pre-packaged tablets of ground coffee have been provided, consisting of a dose of ground coffee contained in a filtering paper bag or sachet, to be placed directly in a filter holder of the espresso coffee machine. These tablets comply with the so called Easy Serving Espresso (E.S.E.) standard. While this arrangement has resulted handy, it is affected by some drawbacks. In particular, the tablet is not air-tight and accordingly a second air-tight packaging must be provided for enclosing each dose, in order to keep the tablet uncontaminated from the external environment during storage.
Moreover, the user's hands come into contact with the tablet when the tablet is placed on the filter holder so that hygiene requirements are not fully assured.
In the past years, disposable capsules containing ground coffee have been also provided. Such capsules, generally having a frustum shape, are made of plastics or aluminum and provide a better air-tight barrier to the external environment than the filtering paper used in tablets.
Known capsules, such as the capsule disclosed in CH-A-605293, have a top surface that is pierceable by an injection needle/nozzle of the espresso coffee machine, in order to inject water under pressure inside the capsule, and a bottom surface comprising weakened zones which tear under pressure of percolation fluids. An internal filter is also provided inside the capsule for preventing solid substances from being ejected from the capsule together with the coffee beverage.
Other known capsules comprise a cylindrical body made of polypropylene, with a top and a bottom surface having a plurality of openings for distributing hot water throughout the dose of ground coffee, and comprising a sheet of paper filter for blocking passage of ground coffee outside the openings of the bottom surface during the extraction phase. These capsules have usually to be placed into a further packaging, such as a multilayered plastic sachet.
In order to prepare a beverage, the known capsules and cartridges are placed into a receptacle that constitutes an extraction chamber. During the extraction phase, the extraction fluid may come into contact with internal surfaces of the extraction chamber before definitively flowing out into the external cup. Such contact contaminates the extraction chamber as well as the filter holder and after a number of coffee extraction operations the quality of the beverage is greatly reduced, suffering from residuals and contaminants in the extraction chamber.
Accordingly, the extraction assembly, comprising the extraction chamber and the filter holder, has to be accurately cleaned after a certain number of coffee extraction operations; in addition, decalcification must be performed on a regular basis.
Even when such cleaning operations are regularly carried out, the fluid turbulence inside the extraction chamber of the machine or the insufficient fluid-tight seal at the opened top surface of the capsule during water injection causes either the extracted beverage or the injected water to lap portions of the external surface of the capsule itself, thus jeopardizing the extraction hygiene requirements.
Another important drawback of known capsules is that they may not retain percolation fluid residuals inside the capsule, in that perforations or openings on the top surface and/or on the bottom surface of the capsules provide for an escape for fluid residuals when the extraction is terminated and/or when the capsule is removed from the machine, causing the capsule to drip and dirty the surroundings of the coffee machine.
Moreover, the beverage obtained from the known capsules is usually easily recognizable by the user as not being a beverage obtained using conventional means, e.g. espresso coffee machines used in bars or pubs, as organoleptic features such as taste, aroma or body, which define the quality of a beverage, are different and even small deviations from the standard quality can be easily perceived during drinking. By way of example, if the beverage is espresso coffee, the cream layer on top of the extraction beverage, which is usually identified with the Italian term “crema”, is immediately felt by the user. If crema is missing, or has a reduced volume or a short life or a pale colour, or it is composed of too large bubbles, the espresso coffee is, even visually, identified as being not good or as a less than optimal espresso, whose quality is below expectation.